The present invention relates to the field of winching systems and in particular, discloses an improved form of winch especially useful for winching cables such as optical fibre communication cables, data cables, power cables, ropes for hauling etc.
There are obviously many uses for winching systems in society. One particular popular use of a winching system is the winching of cables such as optical fibre cables or the like through conduits by workmen in laying down cable systems. Presently, known techniques rely upon a motor system and geared arrangement for driving a capstan around which a cable or lead wire is wrapped. The capstan is then driven by the motor so as to rotate and thereby wind on the cable wire in the usual manner.
Unfortunately, presently utilised systems have a number of disadvantages. In particular, the presently utilised systems have been found to be excessively dangerous in that a wire, under tension is driven by a motor device. Minimal control is placed over the system and hence, as a result of overstressing of equipment, the wire and/or equipment can malfunction which can result in severe bodily injury to persons operating the equipment. Another common problem is overstressing of a cable when too much tension is applied to the cable. The effects applied to a cable through overstressing may in turn cause it to malfunction or to be a of a poor quality. Further, known arrangements for winching of the cables can be excessively dangerous due to imbalances and variations in the forces created by the winching arrangement when driving a cable system.
It is therefore evident that there is a long felt need for a cable hauling system which provides for a safer, more effective operation.
In accordance with a first aspect of the present invention, there is provided a winching arrangement for winching a cable comprising a winching frame; a capstan for winding the cable onto; a drive motor for driving the capstan; and a first mechanical torque limiting mechanism for disengaging the capstan from the drive motor when the torsional load on the capstan exceeds a first predetermined limit.
Preferably, the mechanical torque limiting mechanism comprises a clutch mechanism which is located within the capstan. Ideally, a cone clutch mechanism is used.
Further, their is preferably also provided a second mechanical torque limiting mechanism located adjacent the motor for providing secondary disengagement of the motor from the capstan when the load on the capstan exceeds a second predetermined limit and a gear reducer connected between the capstan and the drive motor.
The winching arrangement as can further include a fixing arm for fixing the winch to an object wherein the cable, the capstan and the fixing arm are aligned substantially concentrically during operation and a capstan support means interconnecting the capstan with a winching frame wherein non torsional forces on the capstan are communicated by the capstan support means to the frame. The capstan support means is preferably interconnected to the frame substantially concentrically with the cable, capstan and fixing arm and the fixing arm is pivotally mounted to the winching frame.
Ideally, the cone clutch is adjustable so as to set the first predetermined limit and located inside the capstan in a sealed tamperproof manner.
In accordance with a second aspect of the present invention, there is provided in a winching arrangement for winching a cable comprising a winching frame; a capstan for winding the cable onto; and a drive motor for driving the capstan, the drive motor driving having a number of active setting and the drive motor only driving the capstan at a predetermined number of the settings; a method of driving the capstan comprising the steps of: activating the drive motor and setting the motor to a non-driving setting; loading the cable on the capstan for haulage by the winching arrangement; setting the drive motor to a driving setting so as to haul the cable.
In one embodiment the number of capstan support means is two. The invention can further include a third mechanical torque limiting device which includes a latching mechanism actuated when the torsional load exceeds a third predetermined limit, the actuation being by a spring loaded strike pin which activates a switch which disables the drive motor.
In one arrangement the capstan includes an internal gear reducer unit for providing a gear reduction driving of the capstan and the capstan is liquid cooled.
In a further modification the arrangement can include a strain gauge for measuring the torsional load on the winching apparatus.
Advantageously, an external roll cage is provided of facilitating convenient and safe operation.